Tamsulosin is a drug approved in the United States for the treatment of signs and symptoms of benign prostatic hyperplasia. It is marketed in an oral formulation under the trade name Flomax®. The R(—) stereoisomer is used for treatment. The approved oral doses are 0.4 mg/day and 0.8 mg/day. The chemical structure of tamsulosin is 5-[2-[[2-(2-ethoxyphenoxy)ethyl]amino]propyl]-2-methoxy-benzenesulfonamide:

Tamsulosin is described in U.S. Pat. No. 5,447,958 to Niigata et al., assigned to Yamanouchi Pharmaceutical Co., Ltd. Therapeutically, it is believed to be an α1-adrenergic receptor antagonist acting preferentially on α1A receptors. While it has therapeutic effects comparable to other α1 antagonists, its benzenesulfonamide structure makes it different chemically from other α1 antagonists in common clinical use (e.g., prazosin and terazosin).
In addition to treatment of signs and symptoms of benign prostatic hyperplasia, tamsulosin has been reported to be effective in the treatment of ureterolithiasis and has been studied as a treatment for painful ejaculation. The use of tamsulosin has also been considered or suggested for other urological conditions, for example evacuatory insufficiency in U.S. Pat. No. 6,861,070 and pathogenic vascular degradative modeling in the ilio-hypogastric-pudendal arterial bed in U.S. Pat. No. 6,787,553.
About twelve years before the present application, the transdermal administration of tamsulosin was taught in U.S. Pat. No. 5,843,472. Certain enhancer combinations are claimed there. It is believed that a permeation enhancer is needed for adequate transdermal administration of tamsulosin.
Despite the teachings of U.S. Pat. No. 5,843,472, there are no tamsulosin patches available in the United States. Transdermal delivery offers well-known advantages in avoiding sharp peak concentrations and side effects resulting from such concentrations. The pharmacokinetics of the oral Flomax® formulation suffers from a considerable food effect, as documented in the package insert. Tamsulosin, like other al antagonists, has produced postural hypotension in some patients, which transdermal delivery may alleviate by avoiding high peak concentrations.
There is therefore a need for an improved transdermal patch which can deliver tamsulosin.